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Does Nitric Oxide Help Or Harm Preemies?

Studies find conflicting results

WEDNESDAY, July 6, 2005 (HealthDay News) -- While significant strides have been made in the care of premature infants, their underdeveloped lungs remain difficult to treat and can cause serious, long-lasting complications.

Two new studies find conflicting results on the use of inhaled nitric oxide as a promising therapy for such tiny babies.

On the plus side, one study found that after two years, premature infants who received nitric oxide had fewer neurodevelopmental problems, such as cerebral palsy, blindness, hearing loss and cognitive problems, than babies who were given a placebo.

But, as encouraging as those findings were, the second and larger study found that nitric oxide therapy didn't increase survival rates for the smallest and sickest premature infants and it didn't decrease their rates of long-term lung disease.

Both studies appear in the July 7 issue of the New England Journal of Medicine.

Despite the findings, most experts still believe that nitric oxide has a place in treating at least some premature infants.

"The potential for nitric oxide therapy is great," said Dr. Michael Schreiber, vice chairman of pediatrics at the University of Chicago and a principal investigator of the positive study. "Nitric oxide helps premature babies, but exactly which babies it helps, we aren't exactly sure yet," he added.

"This is a very promising new treatment for premature infants," said Dr. Richard Martin, director of neonatology at Rainbow Babies and Children's Hospital in Cleveland, and author of an accompanying editorial in the same issue of the journal.

"Nitric oxide, when given appropriately and when we've figured out all of the fine-tuning, has the opportunity for enhancing lung maturation and lung development in these very premature babies," he added.

Nitric oxide is a naturally occurring gas that relaxes the blood vessels and enhances lung growth, according to Martin. It has been shown to help full-term babies at risk of respiratory failure, according to Dr. Krisa Van Meurs, a professor of pediatrics at Stanford University School of Medicine and author of the second study.

Because nitric oxide proved helpful in full-term babies, researchers became interested in using it in premature infants, said Van Meurs, because "the smallest and sickest babies still have significant morbidity and mortality from lung disease."

But, doctors also suspect that nitric oxide may increase premature infants' already elevated risk of bleeding in the brain.

Van Meurs' study looked at 420 premature infants who were born before 34 weeks of gestation and weighed between 401 grams and 1,500 grams -- about 14 ounces to just over three pounds.

All of the babies were in respiratory failure and were randomly assigned to receive either inhaled nitric oxide or a placebo.

The researchers found that nitric oxide wasn't any more effective than a placebo in treating these very sick babies. However, when the researchers separated the babies according to weight, they did see a benefit in larger babies. There was a 19 percent decrease in the risk of death or lung disease, according to the study.

"Bigger infants -- over 1,000 grams -- benefited with decreased mortality and decreased lung disease," said Van Meurs.

As doctors have feared, the risk of bleeding in the brain was 10 percent higher in the smallest babies.

"This study helps us begin to put boundaries on this new therapy," said Schreiber of Van Meurs' study.

Schreiber's study, which he said included a healthier group of preemies, followed 138 premature infants who had received either nitric oxide or a placebo for two years. He said initial results, which were previously published, showed a decrease in mortality and in lung disease for the nitric oxide group.

The current study was designed to measure the babies' neurodevelopmental outcomes two years after they received treatment. The researchers found that nitric oxide treatment cut the risk of neurodevelopmental problems in half -- 24 percent of the nitric oxide group versus 46 percent of the placebo group had neurodevelopmental impairments.

Several factors account for the differences in the two studies' findings, said Martin. The biggest is that the babies in Van Meurs' study were much sicker. Schreiber also pointed out that in his study, the average treatment was for seven days versus three days for the Van Meurs study.

Another possibility and an "intriguing" one, according to both Martin and Schreiber, is a difference in race. In Schreiber's study, 63 percent of the babies treated with nitric oxide were black, while only 33 percent in the Van Meurs study were black.

Martin pointed out that in the Nov. 11, 2004, issue of the New England Journal of Medicine, researchers reported that the drug isosorbide dinitrate plus hydralazine was more effective in preventing heart failure in black patients. Interestingly, said Martin, that drug makes nitric oxide more available in the body.

Both Schreiber and Van Meurs said the possibility of a racial difference in treatment occurred to them, but neither study showed a strong difference when broken down by race. However, the number of babies in each group may be too small to see such a difference, said Schreiber.

All three agreed that more studies need to be done, and several larger trials are just beginning. So, for now, nitric oxide will continue to be studied and won't be universally available for parents of premature infants, noted Schreiber.

More information

To learn what you can do to prevent having a premature baby, visit the March of Dimes.

SOURCES: Richard Martin, M.D., director, neonatology, Rainbow Babies and Children's Hospital, and professor of pediatrics, Case School of Medicine, Cleveland; Krisa Van Meurs, M.D., professor of pediatrics, Stanford University School of Medicine, Palo Alto, Calif.; Michael Schreiber, M.D., vice chairman of pediatrics, University of Chicago; July 7, 2005, New England Journal of Medicine
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